Bushmaster223
Member
Hey can someone give me the optimum bullet weights to twist rate?
twist rate to bullet weight
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Hey can someone give me the optimum bullet weights to twist rate?jim147
Member
There are a few formulas but they are based on older bullet designs.
I think bullet length and construction are much more important than weight.
What are you wanting to do?
You may get a better answer that way.
jim
I think bullet length and construction are much more important than weight.
What are you wanting to do?
You may get a better answer that way.
jim
Bushmaster223
Member
Thanks guys. I am trying to decide on 150 gr. or 168 gr. bullets in my .308 with 24 in. barrel and 1:10 twist rate
ArchAngelCD
Member.
With a 1:10 twist you could probably stabilize a 175gr or even a 180gr bullet so I see no reason not to use a 168gr bullet if you are looking for the weight.
The Greenhill formula is as follows:
Where,
C = 150 (a constant for bullets up to 2,800 fps, use C=180 for bullets over 2,800 fps)
D = bullet diameter e.g. .308"
L = length of the bullet e.g. 168gr SMK HPBT is 1.210"
SG = specific gravity of the material from which the bullet is made e.g. lead = 11.35 (it's a ratio so it has no units) but for lead core bullets use 10.9 which conveniently cancels out the square root term. If you use 11.35 as the SG for lead, the twist rates are about 0.2 inches higher.
Therefore, based on the Greenhill formula, the "ideal" twist rate for a 168gr SMK HPBT with a length of 1.210" is 1:11.8. A 190gr SMK has a length of about 1.360" and so a 1:10.4 is the "ideal" twist rate for that bullet.
That said, I shoot a 168gr Nosler HPBT custom competition bullet out of a 1:10 barrel with very good results so I agree with ArchAngelCD, shoot the 168gr. I shoot a Hornady A-MAX 208gr bullet out of my .300 Win Mag and that also has a 1:10 twist. According to the Greenhill formula, the ideal twist rate for the A-MAX is 1:10 (using C = 150). That works really well too.
Where,
C = 150 (a constant for bullets up to 2,800 fps, use C=180 for bullets over 2,800 fps)
D = bullet diameter e.g. .308"
L = length of the bullet e.g. 168gr SMK HPBT is 1.210"
SG = specific gravity of the material from which the bullet is made e.g. lead = 11.35 (it's a ratio so it has no units) but for lead core bullets use 10.9 which conveniently cancels out the square root term. If you use 11.35 as the SG for lead, the twist rates are about 0.2 inches higher.
Therefore, based on the Greenhill formula, the "ideal" twist rate for a 168gr SMK HPBT with a length of 1.210" is 1:11.8. A 190gr SMK has a length of about 1.360" and so a 1:10.4 is the "ideal" twist rate for that bullet.
That said, I shoot a 168gr Nosler HPBT custom competition bullet out of a 1:10 barrel with very good results so I agree with ArchAngelCD, shoot the 168gr. I shoot a Hornady A-MAX 208gr bullet out of my .300 Win Mag and that also has a 1:10 twist. According to the Greenhill formula, the ideal twist rate for the A-MAX is 1:10 (using C = 150). That works really well too.
Last edited:
rcmodel
Member in memoriam
A 1/10 .308 will stabilize up to at least a 200, and probably a 220.
There is nothing to even worry about between a 150 and a 168.
Just pick whatever one you want to use and Fogadabout the twist.
It is a non-issue.
For many years, since 1903 in fact, 1/10 twist has been the standerd used in the 30-06.
.308 was always 1/12.
If you have a 1/10 .308, you have the perfect twist for any bullet weight you wish to use in it.
rc
There is nothing to even worry about between a 150 and a 168.
Just pick whatever one you want to use and Fogadabout the twist.
It is a non-issue.
For many years, since 1903 in fact, 1/10 twist has been the standerd used in the 30-06.
.308 was always 1/12.
If you have a 1/10 .308, you have the perfect twist for any bullet weight you wish to use in it.
rc
dagger dog
Member
Check stevespages.com he has an updated version of the Greenhill formula.
The Yahoo search engine will work for stevespages but the AOL Google won't!
The Yahoo search engine will work for stevespages but the AOL Google won't!
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